Photovoltaic systems representation for high frequency studies - part II: The inverter modeling

The ultra fast variations present in the voltage output of PWM inverters are responsible for several problems in the scope of electromagnetic compatibility. In the case of photovoltaic systems, which is the subject of this work, the major concern relies on the common mode voltage produced by the inverter, whose fast dv/dt's excite all the distributed capacitances of the system devices to the ground, generating unwanted high-frequency currents flowing through different paths. Among other problems, these currents generate conducted electromagnetic interference. The loops for their circulation include the capacitive coupling between (i) the solar cells and the corresponding module frame, (ii) the cable phase conductors and the trays or metallic tubes where they are installed, (iii) internal parts of the transformer and filters and their frame and (iv) the inverter internal devices and the grounded heatsink. In this work, the focus is on the appropriate modeling of the inverter for electromagnetic compatibility studies. A special effort was employed on the development of a measuring methodology of the models parameters, suitable for application in the field.